Just two days after Microsoft relaunched its YouTube app for Windows Phone smartphones and thanked Google for its "support", Google has once again blocked the app from working.

The app had originally been removed from the Windows Phone store in May after Google complained to Microsoft about its ability to download videos to the device, as well as preventing video advertisements from playing.

It relaunched this week, but now Google has blocked it again. "Microsoft has not made the browser upgrades necessary to enable a fully-featured YouTube experience, and has instead re-released a YouTube app that violates our Terms of Service," a spokesperson tells The Verge.

"It has been disabled. We value our broad developer community and therefore ask everyone to adhere to the same guidelines."

Google's views contradict Microsoft's public statements after the app was relaunched on Tuesday (13 August), when the company said it "provides the great experience our consumers expect while addressing the concerns Google expressed in May, including the addition of ads".

At the time, Microsoft also talked about "Google's support in ensuring that Windows Phones customers have a quality YouTube experience" and expressed hopes for "continuing the collaboration".

Those prospects seem somewhat less hopeful now. Microsoft later published a longer blog post by its vice president and deputy general counsel, David Howard, explaining exactly why the app has been blocked again.

According to Howard, Microsoft bowed to Google's wishes by re-enabling ads, removing the ability for users to download videos, and also stopping them from watching "reserved" videos on YouTube.

"There was one sticking point in the collaboration. Google asked us to transition our app to a new coding language – HTML5. This was an odd request since neither YouTube's iPhone app nor its Android app are built on HTML5. Nevertheless, we dedicated significant engineering resources to examine the possibility.

At the end of the day, experts from both companies recognized that building a YouTube app based on HTML5 would be technically difficult and time consuming, which is why we assume YouTube has not yet made the conversion for its iPhone and Android apps."

Microsoft went ahead and re-published its non-HTML5 YouTube app for Windows Phone while "committing to work with Google long-term on an app based on HTML5", but Howard says Google decided to block the short-term app nonetheless.

"It seems to us that Google's reasons for blocking our app are manufactured so that we can't give our users the same experience Android and iPhone users are getting," wrote Howard. "The roadblocks Google has set up are impossible to overcome, and they know it."

Howard's blog post concludes with a request for Google to stop blocking the app, although there are more menacing hints elsewhere in the post when he refers to antitrust investigations against Google ("some of which are still ongoing") where the company "has reiterated its commitment to openness and its ability to stick to its openness commitments voluntarily".

It remains to be seen whether the current spat finds its way into a future antitrust complaint. It's not the first time YouTube has been a pawn in wider clashes between Microsoft and other big technology companies.

YouTube used to be preloaded in Apple's iOS software for iPhones and iPads, but was removed from iOS 6 and onwards due to Google and Apple's licensing deal not being renewed. Google later launched a standalone version of the app through Apple's App Store.

Mobile is increasingly important to YouTube, accounting for more than 25% of its global watch time, and more than 1bn views a day.